The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, gas regulators are implemented into these distribution systems to ensure that the delivered gas meets the requirements of the end-user facilities. Conventional gas regulators generally include a closed-loop control actuator for sensing and controlling the pressure of the delivered gas.
FIG. 1 depicts one conventional gas regulator 10. The regulator 10 generally comprises an actuator 12 and a regulator valve 14. The regulator valve 14 defines an inlet 16 for receiving gas from a gas distribution system, for example, and an outlet 18 for delivering gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances, for example. Additionally, the regulator valve 14 includes a valve port 36 disposed between the inlet and the outlet. Gas must pass through the valve port 36 to travel between the inlet 16 and the outlet 18 of the regulator valve 14.
The actuator 12 is coupled to the regulator valve 14 to ensure that the pressure at the outlet 18 of the regulator valve 14, i.e., the outlet pressure, is in accordance with a desired outlet or control pressure. The actuator 12 is therefore in fluid communication with the regulator valve 14 via a valve mouth 34 and an actuator mouth 20. The actuator 12 includes a control assembly 22 for regulating the outlet pressure of the regulator valve 14 based on sensed outlet pressure. Specifically, the control assembly 22 includes a diaphragm supporting plate 19, a diaphragm 24, a piston 32, and a control arm 26 having a valve disc 28. The valve disc 28 includes a generally cylindrical body 25 and a sealing insert 29 fixed to the body 25. The diaphragm 24 senses the outlet pressure of the regulator valve 14 and provides a response to move the valve disc 28 to open and close the regulator valve 14. The control assembly 22 further includes a control spring 30 in engagement with a top-side of the control assembly 22 to offset the outlet pressure sensed by the diaphragm 24. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure, is set by the selection of the control spring 30.
The diaphragm 24 is operably coupled to the control arm 26, and therefore, the valve disc 28, via the piston 32, and controls the opening of the regulator valve 14 based on the sensed outlet pressure. For example, when an end user operates an appliance, such as a furnace, for example, that places a demand on the gas distribution system downstream of the regulator 10, thereby decreasing the outlet pressure. Accordingly, the diaphragm 24 senses this decreased outlet pressure. This allows the control spring 30 to expand and move the piston 32 and the right-side of the control arm 26 downward, relative to the orientation of FIG. 1. This displacement of the control arm 26 moves the valve disc 28 away from the valve port 36 to open the regulator valve 14, thereby increasing the outlet flow to meet the increased demand from the appliance and increasing the outlet pressure back to the control pressure. So configured, the appliance may draw gas through the valve port 36 and through the outlet 18 of the regulator valve 14.
In the conventional regulator 10, the control spring 30 inherently generates less force as it expands towards an uncompressed length when displacing the control arm 26 to open the valve port 36. Additionally, as the control spring 30 expands, the diaphragm 24 deforms, which increases the area of the diaphragm 24. The decreased force supplied by the control spring 30 and the increased area of the diaphragm 24 in this operational scenario combine to create a regulator response wherein the force provided by the control spring 30 cannot adequately balance the force generated by the diaphragm 24 thereby resulting in an outlet control pressure that is less than that originally set by the user. This phenomenon is known as “droop.” When “droop” occurs, the outlet pressure decreases below its set control pressure and the regulator 10 may not function as intended. “Droop” is one example of the detrimental effects of the dynamic pressures that may arise within a regulator 10.
To counteract such effects, some conventional regulators 10 include a pressure sense tube 15. The sense tube 15 may include a straight sense tube 15a, as illustrated in solid lines in FIG. 1, or may include a bent sense tube 15b, as illustrated in phantom. Either sense tube 15a, 15b includes an elongated cylindrical tube with an open, sensing end 17a, 17b. The open end 17a, 17b is configured to sense the pressure of the gas at the outlet 18 of the regulator valve 14, and the tubes 15a, 15b are adapted to transmit the sensed pressure to the diaphragm 24. Thus, the sense tubes 15a, 15b provide a more accurate detection of the pressure at the outlet 18 of the regulator valve 14, than the diaphragm 24 would otherwise sense. Operating without a sense tube 15a, 15b often leads to pressure higher than the downstream pressure being sensed by the diaphragm 24, due to dynamic pressure effects.
For example, with reference to FIGS. 2 and 3, as the flow of gas emerges from the valve port 36 and expands, it travels downstream and over the sense tube 15a, 15b. This creates three regions of pressure. The three regions include a Low Pressure Region (LPR) 301, a Medium Pressure Region (MPR) 303, and a High Pressure Region (HPR) 305.
The conventional sense tubes 15a, 15b depicted in FIGS. 2 and 3, as mentioned above, have open ends 17a, 17b. The open ends 17a, 17b only communicate pressure from the LPRs 301 to the diaphragm 24 of the actuator 12 depicted in FIG. 1. The pressure within the LPRs 301 decreases proportionately to the flow over the sense tubes 15a, 15b. As flow increases, the pressure within the LPRs 301 begins to deviate significantly from the true downstream pressure, thereby providing an increasingly inaccurate detection of pressure to the diaphragm 24 of the actuator 12. This can lead to the diaphragm 24 responding to a pressure that is lower than the actual outlet pressure, which may be undesirable.
Referring back to FIG. 1, the control assembly 22 of the conventional regulator 10 further functions as a relief valve. Specifically, the control assembly 22 also includes a relief spring 40 and a release valve 42. The diaphragm 24 includes an opening 44 through a central portion thereof and the piston 32 includes a sealing cup 38. The relief spring 40 is disposed between the piston 32 and the diaphragm 24 to bias the diaphragm 24 against the sealing cup 38 to close the opening 44, during normal operation. Upon the occurrence of a failure such as a break in the control arm 26, the control assembly 22 is no longer in direct control of the valve disc 28 and inlet flow will move the valve disc 28 into an extreme open position. This allows a maximum amount of gas to flow into the actuator 12. Thus, as the gas fills the actuator 12, pressure builds against the diaphragm 24 forcing the diaphragm 24 away from the sealing cup 38, thereby exposing the opening 44. The gas therefore flows through the opening 44 in the diaphragm 24 and toward the release valve 42. The release valve 42 includes a valve plug 46 and a release spring 54 biasing the valve plug 46 into a closed position, as depicted in FIG. 1. Upon the pressure within the actuator 12 and adjacent the release valve 42 reaching a predetermined threshold pressure, the valve plug 46 displaces upward against the bias of the release spring 54 and opens, thereby exhausting gas into the atmosphere and reducing the pressure in the regulator 10. The sense tube 15 may also assist the regulator 10 in providing this relief function by providing a signal representative of the actual outlet pressure to the diaphragm 24 of the actuator 12. However, as mentioned above, the pressure sensed by the conventional sense tube 15 under high flow conditions, for example, may be inaccurate.